Auto: abcip-5.1 — HSBY paired-IP role probing

Closes #242

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriverFactoryExtensions.cs

@@ -43,7 +43,15 @@ public static class AbCipDriverFactoryExtensions
                         "AddressingMode", fallback: AddressingMode.Auto),
                     ReadStrategy: ParseEnum<ReadStrategy>(d.ReadStrategy, "device", driverInstanceId,
                         "ReadStrategy", fallback: ReadStrategy.Auto),
-                    MultiPacketSparsityThreshold: d.MultiPacketSparsityThreshold ?? 0.25))]
+                    MultiPacketSparsityThreshold: d.MultiPacketSparsityThreshold ?? 0.25,
+                    // PR abcip-5.1 — HSBY paired-IP knobs. Both null / absent = no HSBY.
+                    PartnerHostAddress: d.PartnerHostAddress,
+                    Hsby: d.Hsby is null ? null : new AbCipHsbyOptions
+                    {
+                        Enabled = d.Hsby.Enabled ?? false,
+                        RoleTagAddress = d.Hsby.RoleTagAddress ?? "WallClockTime.SyncStatus",
+                        ProbeInterval = TimeSpan.FromMilliseconds(d.Hsby.ProbeIntervalMs ?? 2_000),
+                    }))]
                 : [],
             Tags = dto.Tags is { Count: > 0 }
                 ? [.. dto.Tags.Select(t => BuildTag(t, driverInstanceId))]
@@ -163,6 +171,32 @@ public static class AbCipDriverFactoryExtensions
         ///     resolves to <c>Auto</c>. Default <c>0.25</c>; clamped to <c>[0..1]</c>.
         /// </summary>
         public double? MultiPacketSparsityThreshold { get; init; }
+
+        /// <summary>
+        ///     PR abcip-5.1 — canonical AB CIP gateway URI of the partner chassis in a
+        ///     ControlLogix HSBY pair. <c>null</c> = no HSBY partner; the driver behaves
+        ///     exactly like every pre-5.1 build. When set together with
+        ///     <see cref="Hsby"/> <c>.Enabled = true</c>, the driver runs a second probe loop
+        ///     against the partner + reports the active chassis through driver diagnostics.
+        /// </summary>
+        public string? PartnerHostAddress { get; init; }
+
+        /// <summary>
+        ///     PR abcip-5.1 — HSBY (Hot-Standby) sub-options. Defaults to
+        ///     <c>Enabled = false</c> when omitted; pre-5.1 deployments are unaffected.
+        /// </summary>
+        public AbCipHsbyDto? Hsby { get; init; }
+    }
+
+    /// <summary>
+    ///     PR abcip-5.1 — JSON-mirror of <see cref="AbCipHsbyOptions"/>. Off by default; enabled
+    ///     by setting <c>Enabled = true</c> + the parent device's <c>PartnerHostAddress</c>.
+    /// </summary>
+    internal sealed class AbCipHsbyDto
+    {
+        public bool? Enabled { get; init; }
+        public string? RoleTagAddress { get; init; }
+        public int? ProbeIntervalMs { get; init; }
     }
 
     internal sealed class AbCipTagDto